Method of controlling electric oil pump in hybrid vehicle

ABSTRACT

A method of controlling an electric oil pump in a hybrid vehicle controls, at an ultra-low temperature, the electric oil pump so that the number of revolutions thereof is not unnecessarily increased, so as to prevent unnecessary power consumption of the battery, thereby contributing to an increase in fuel efficiency, to prevent unnecessary noise, thereby improving the market quality of the vehicle, and to improve the endurance of the electric oil pump.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority of Korean Patent ApplicationNumber 10-2011-0131872 filed Dec. 9, 2011, the entire contents of whichapplication is incorporated herein for all purposes by this reference.

BACKGROUND OF INVENTION

1. Field of Invention

The present invention relates, in general, to a method of controlling anelectric oil pump in a hybrid vehicle and, more particularly, to amethod of controlling an electric oil pump at an ultra-low temperature.

2. Description of Related Art

A hybrid vehicle is provided with an electric oil pump, which canoperate irrespective of the operation of an engine, in addition to amechanical oil pump, which is provided inside a transmission, so thathydraulic pressure necessary for the transmission can be supplied evenin a situation in which, for example, the engine does not operate.

The above-mentioned method of controlling an electric oil pump of therelated art is generally carried out as shown in FIG. 1. The electricoil pump is controlled following a target number of revolutions that isprovided from a transmission control unit (TCU). In order to ensureresponsibility at an early stage of the startup of the electric oilpump, the electric oil pump is controlled in an open loop up to apredetermined reference number of revolution, thereby rapidly increasingthe number of revolution of the electric oil lamp. Once the number ofrevolutions exceeds the reference number of revolutions, closed loopcontrol mode is performed by following the target number of revolutionsthat is provided from the TCU.

In the control method as described above, the reference number ofrevolutions is set in consideration of the viscosity of oil of thetransmission, so that an intended oil pressure can be rapidly built up.

However, in an ultra-low-temperature state, such as at −10° C. or less,the viscosity of the oil is relatively greater than that of the oil atroom temperature, a sufficient amount of oil pressure can be built upeven if the electric oil pump is rotated at a relatively small number ofrevolutions.

Therefore, in the ultra-low-temperature state, it may be inappropriateto control the electric oil pump, which is set to the room temperaturestate, in an open loop up to a reference number of revolutions.

As shown in FIG. 2, when the reference number of revolutions that isappropriately set to the room temperature state is 500 RPM, even if thetarget number of revolutions provided from the TCU is merely 300 RPM atan early stage, the electric oil pump is controlled in an open loop upto the reference number of revolutions of 500 RPM by the same method asthat of the related art. Only after the number of revolutions hasreached the reference number of revolutions, performed is a closed loopcontrol mode, which follows the target number of revolutions. Thisconsequently leads to a situation in which the number of revolutions ofthe electric oil pump is unnecessarily increased, as indicated by “A” inFIG. 2.

When the number of revolutions of the electric oil pump is needlesslyincreased like this, the battery unnecessarily consumes electricalpower, resulting in an adverse effect on fuel efficiency. In particular,this unnecessarily causes noise, thereby reducing the market quality ofa vehicle, and is undesirable for the endurance of the vehicle, which isproblematic.

An exemplar of the related art is Korean Patent Application No. KR10-2009-0045990 A.

The information disclosed in this Background section is only forenhancement of understanding of the general background of the inventionand should not be taken as an acknowledgement or any form of suggestionthat this information forms the prior art already known to a personskilled in the art.

SUMMARY OF INVENTION

Various aspects of the present invention provide for a method ofcontrolling an electric oil pump in a hybrid vehicle, in which theelectric oil pump is controlled so that the number of revolutionsthereof is not unnecessarily increased at an ultra-low temperature, soas to prevent unnecessary power consumption of the battery, therebycontributing to an increase in fuel efficiency, to prevent unnecessarynoise, thereby improving the market quality of the vehicle, and toimprove the endurance of the electric oil pump.

Various aspects of the present invention provide for a method ofcontrolling an electric oil pump in a hydraulic vehicle. The methodincludes the steps of: measuring an oil temperature of a transmission;determining whether or not the oil temperature of the transmission is anultra-low temperature that does not exceed a predetermined referencetemperature; controlling the electric oil pump in an open loop up to atarget number of revolutions when the oil temperature of thetransmission is the ultra-low temperature as a result of the step ofdetermining whether or not the oil temperature of the transmission is anultra-low temperature; and controlling the electric oil pump in a closedloop in order to follow the target number of revolutions after the stepof controlling the electric oil pump in the open loop is ended.

At an ultra-low temperature, the electric oil pump of the hybrid vehiclemay be controlled so that the number of revolutions thereof is notunnecessarily increased, so as to prevent unnecessary power consumptionof the battery, thereby contributing to an increase in fuel efficiency,to prevent unnecessary noise, thereby improving the market quality ofthe vehicle, and to improve the endurance of the electric oil pump.

The methods and apparatuses of the present invention have other featuresand advantages which will be apparent from or are set forth in moredetail in the accompanying drawings, which are incorporated herein, andthe following Detailed Description, which together serve to explaincertain principles of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing a process of the related art, which controlsan electric depicting pump at room temperature.

FIG. 2 is a graph depicting a process of the related art, which controlsan electric depicting pump at ultra-low temperature.

FIG. 3 is a process view depicting an exemplary method of controlling anelectric oil pump in a hybrid vehicle according to the presentinvention.

FIG. 4 is a graph depicting an exemplary process of controlling anelectric oil pump at ultra-low temperature according to the presentinvention.

DETAILED DESCRIPTION

Reference will now be made in detail to various embodiments of thepresent invention(s), examples of which are illustrated in theaccompanying drawings and described below. While the invention(s) willbe described in conjunction with exemplary embodiments, it will beunderstood that present description is not intended to limit theinvention(s) to those exemplary embodiments. On the contrary, theinvention(s) is/are intended to cover not only the exemplaryembodiments, but also various alternatives, modifications, equivalentsand other embodiments, which may be included within the spirit and scopeof the invention as defined by the appended claims.

Referring to FIG. 3, a method of controlling an electric oil pump in ahybrid vehicle according to various embodiments of the inventionincludes oil temperature-measuring step S10 of measuring the oiltemperature of a transmission, ultra-low temperature determination stepS20 of determining whether or not the oil temperature of thetransmission is an ultra-low temperature that does not exceed apredetermined reference temperature, first open loop control step S30 ofcontrolling the electric oil pump in an open loop up to the targetnumber of revolutions, and closed loop control step S40 of controllingthe electric oil pump in a closed loop in order to follow the targetnumber of revolutions.

When the operation of the electric oil pump is started at anultra-low-temperature state, the electric oil pump is notunconditionally controlled in an open loop up to a predeterminedreference number of revolutions unlike the related art. Rather, theelectric oil pump is controlled in the open loop up to a target numberof revolutions that is provided from a transmission control unit (TCU),and after that, is controlled in a closed loop. This consequentlyexcludes an excessive initial operation, which exceeds the target numberof revolutions, from the electric oil pump, thereby increasing fuelefficiency by preventing unnecessary energy consumption, decreasingnoise, and helping to improve the durability of the electric oil pump.

The predetermined reference temperature in the ultra-low temperaturedetermination step S20 is set in consideration of the effect that achange in the viscosity of oil in the transmission takes on theformation of oil pressure in response to the operation of the electricoil pump. In various embodiments, the reference temperature may be setin the range of at least −10° C. or less.

As a result of the ultra-low temperature determination step S20, when itis not the ultra-low-temperature state, the second open loop controlstep S50 is performed to control the electric oil pump in an open loopup to the predetermined reference number of revolutions, and then theclosed loop control step S40 is performed after the second open loopcontrol step S50.

That is, the second open loop control step S50 is the same as a controlmethod of the related art in a common situation.

Therefore, the reference number of revolutions in the second open loopcontrol step S50 is set in consideration of the responsibility of theelectric oil pump based on the room temperature state, and is a numberof revolutions that is higher than the target number of revolutions inthe first open loop control step S30.

That is, for example, as shown in FIG. 4, when the reference number ofrevolutions is set at 500 RPM in consideration of the viscosity of thetransmission oil at room temperature and in consideration of theresponsibility following the start-up of the electric oil pump, thetarget number of revolutions that is calculated and presented by the TCUat the first open loop control step S30 is a number of revolutions thatis of course smaller than the reference number of revolutions. Therelatively high target number of revolutions at the early stage of thestartup of the electric oil pump is 300 RPM that is smaller than thereference number of revolutions 500 RPM. This conversely means that thereference number of revolutions is set to be greater than the targetnumber of revolutions in the first open loop control step S30.

The open loop control can be performed in duty control mode in whichonly a duty value is provided to the motor of the electric oil pump,whereas the closed loop control can be performed in proportionalintegration (PI) control mode in which the target number of revolutionsis followed by feeding back the number of revolutions of the electricoil pump. Of course, in addition to the above,proportional/integral/derivative control (PID) mode or the like may beused as a particular method of closed loop control.

When comparing FIG. 4 with FIG. 2, it can be appreciated that anovershoot at the early stage of the operation of the electric oil pumpis solved, and that the number of revolutions of the electric oil pumpis not unnecessarily increased. Accordingly, it is of course possible toincrease the fuel efficiency of a vehicle, reduce noise in the vehicle,and increase the durability of the electric oil pump.

For convenience in explanation and accurate definition in the appendedclaims, the terms upper or lower, front or rear, inside or outside, andetc. are used to describe features of the exemplary embodiments withreference to the positions of such features as displayed in the figures.

The foregoing descriptions of specific exemplary embodiments of thepresent invention have been presented for purposes of illustration anddescription. They are not intended to be exhaustive or to limit theinvention to the precise forms disclosed, and obviously manymodifications and variations are possible in light of the aboveteachings. The exemplary embodiments were chosen and described in orderto explain certain principles of the invention and their practicalapplication, to thereby enable others skilled in the art to make andutilize various exemplary embodiments of the present invention, as wellas various alternatives and modifications thereof. It is intended thatthe scope of the invention be defined by the Claims appended hereto andtheir equivalents.

What is claimed is:
 1. A method of controlling an electric oil pump in ahydraulic vehicle, comprising: measuring an oil temperature of atransmission; determining whether or not the oil temperature of thetransmission is an ultra-low temperature that does not exceed apredetermined reference temperature; controlling the electric oil pumpin an open loop up to a target number of revolutions when it isdetermined that the oil temperature of the transmission is the ultra-lowtemperature; and controlling the electric oil pump in a closed loop inorder to follow the target number of revolutions after the controllingthe electric oil pump in the open loop is ended.
 2. The method of claim1, wherein the predetermined reference temperature is in a range of −10°C. or less, in consideration of an effect that a change in a viscosityof oil in the transmission takes on a formation of oil pressure inresponse to an operation of the electric oil pump.
 3. The method ofclaim 1, further comprising: when the oil temperature of thetransmission is not the ultra-low temperature, controlling the electricoil pump up to a reference number of revolutions in an open loop; andperforming the controlling the electric oil pump in a closed loop afterthe controlling the electric oil pump up to a reference number ofrevolutions in an open loop.
 4. The method of claim 3, wherein thereference number of revolutions at the controlling the electric oil pumpup to a reference number of revolutions in an open loop is set inconsideration of a responsibility of the electric oil pump based on aroom temperature state, such that the reference number of revolutions isgreater than a target number of revolutions at the controlling theelectric oil pump in an open loop up to a target number of revolutions.5. The method of any one of claim 1, wherein the controlling theelectric oil pump in an open loop is performed in duty control mode, inwhich only a duty value is provided to a motor of the electric oil pump,and the controlling the electric oil pump in a closed loop is performedin proportional integration control mode, in which the target number ofrevolutions is followed by feeding back a number of revolutions of theelectric oil pump.
 6. The method of any one of claim 2, wherein thecontrolling the electric oil pump in an open loop is performed in dutycontrol mode, in which only a duty value is provided to a motor of theelectric oil pump, and the controlling the electric oil pump in a closedloop is performed in proportional integration control mode, in which thetarget number of revolutions is followed by feeding back a number ofrevolutions of the electric oil pump.
 7. The method of any one of claim3, wherein the controlling the electric oil pump in an open loop isperformed in duty control mode, in which only a duty value is providedto a motor of the electric oil pump, and the controlling the electricoil pump in a closed loop is performed in proportional integrationcontrol mode, in which the target number of revolutions is followed byfeeding back a number of revolutions of the electric oil pump.
 8. Themethod of any one of claim 4, wherein the controlling the electric oilpump in an open loop is performed in duty control mode, in which only aduty value is provided to a motor of the electric oil pump, and thecontrolling the electric oil pump in a closed loop is performed inproportional integration control mode, in which the target number ofrevolutions is followed by feeding back a number of revolutions of theelectric oil pump.